DTE Energy Co.'s DTE Mainstream is to buy a natural gas gathering system and gathering pipeline in Louisiana for a total of $2.65 billion.

DTE Energy Co. unit DTE Midstream agreed to buy a natural gas gathering system and gathering pipeline in the Haynesville Shale rock formation in Louisiana for $2.25 billion in cash, plus another $400 million at a 2020 milestone.

Detroit-based DTE will take on all assets from Momentum Midstream and Indigo Natural Resources, the main natural gas producer supplying the system, including a 150-mile, under-construction pipeline and an existing gathering system.

DTE (NYSE: DTE) made the announcement in a news release Friday morning. It gives DTE access to growing markets around the Gulf Coast, the release said.

DTE Midstream is the utility company's natural gas storage, pipeline and gathering provider in the Midwest, Appalachian area, the Northeast and in Ontario. It said in May it would acquire an additional 30 percent of Stonewall Gas Gathering in West Virginia for $275.3 million. DTE wants to spend $4 billion-$5 billion in its midstream business between this year and 2023.

"DTE's non-utility operations continue to grow, perform well and fit nicely into our planned utility and non-utility mix," Jerry Norcia, president and CEO of DTE Energy, said in the release. "This acquisition significantly enhances the strength and diversity of DTE Midstream, adding premium assets in one of the fastest growing and best positioned U.S. shale formations. The successful operation of the Link asset, also purchased from Momentum, demonstrates the operating expertise and value creation DTE Midstream brings to this new system. In addition, the company gains a strong commercial partner in Indigo, one of the nation's largest private natural gas producers supplying the rapidly growing demand in the Gulf Coast region."

DTE Energy Co.

A map shows the assets to be purchased by DTE Energy Co.'s DTE Mainstream.

The deal is expected to close in the fourth quarter, pending closing conditions and regulatory approvals, the release said. The additional $400 million would be paid when the under-construction pipeline is finished in the third or fourth quarter of 2020.

DTE's stock price was $129.48 per share as of Thursday's close. That is up slightly over the course of the week from $128.11 Monday, but down from $131.63 a month ago.

The Haynesville Shale is a sedimentary rock layer 10,000 feet under the earth's surface, spread across northwestern Louisiana, southwestern Arkansas and eastern Texas, according to the State of Louisiana's website. Some energy companies have started work to drill for natural gas there, "based on findings indicating a potentially large supply of gas trapped within some portions of the shale," the website said. Exploring Haynesville was previously considered too expensive, but as energy costs increase and technology evolves, it is seeming more viable, and activity there has grown.

"In light of that (attention), the value landowners are able to get for selling leases has risen sharply," the website said.